The MTBA has adopted the following bat usage rules for Recreation and Travel Baseball:

Tee-Ball through Majors (ages 4-12)

Composite barrel bats are not allowed to be used in any Recreation games in the Tee-Ball through Majors divisions (ages 4-12); "big barrel" bats (exceeding 2 1/4" diameter) are also not allowed for any Recreation games in these divisions; all other bats may be used in recreation games provided they meet the official Babe Ruth League specifications (link to that below)

Per the documented MTBA recreation rules, if an illegal bat is identified it needs to be immediately removed from the game (whether noticed by a player, coach, manager, or umpire); the umpire does not need to make this ruling, the aforementioned should be proactive and remove the bat if noticed, but the umpire may be asked to rule on a bat by a manager or coach (whether it is on one of their own player's bats or an opponent's) if they are unsure; if the composition of the barrel on a bat in question cannot be clearly identified on the bat itself then it should be removed from play (safety first!)

All bats, including those with composite barrels, meeting the specifications set out by Babe Ruth League (for Babe Ruth/Cal Ripken League sanctioned tournaments) or by the individual league/tournament rules may be used by 12U and younger MTBA Travel teams in their travel league/tournament games

Pony Division (ages 13-15)

Composite barrel bats are allowed to be used in Recreation Pony division games provided that the bat meets the official Babe Ruth League specifications

All bats meeting the specifications set out by Babe Ruth League (for Babe Ruth/Cal Ripken League sanctioned tournaments) or by the individual league/tournament rules may be used by 13U and older MTBA Travel teams in their travel league/tournament games